This invention relates generally to the optical components used in optical communication networks, and specifically to a hybrid optical module that combines an electrically-tunable optical filter, optical source(s) and a novel lens unit.
Optical communication networks are built by combining sub-systems, modules, or components which perform specific functions, including the function of selecting or removing a particular wavelength or group of wavelengths. Briefly, multiple optical signals can be transmitted simultaneously by encoding them in separate carrier wavelengths similar to the way radio stations use different carrier frequencies to which the end user tunes. Encoding multiple signals using different carrier wavelengths is referred to as Dense Wavelength Division Multiplexing (DWDM). A general description of optical networking functions and applications can be found in “Introduction to DWDM Technology”, by S. Kartalopoulos, Wiley-Interscience, 2000. In this application, “multiple” means “more than one.”
DWDM Technology has been widely deployed in long haul communications networks. Recently, this technology started migrating to short-haul optical communications networks, for applications such as Digital TV delivery, Fiber-to-the-Home (FTTH), Internet access, Local Area Networks, back-haul connections for cellular base stations, Wi-Fi hotspots, and other forms of broadband access. In prior networks, it has been typical for only one specified wavelength to reach the receiver of an end user, who also sends a single wavelength back to the network. This transmitter-receiver (transceiver) module at the end user is called a bi-directional wavelength add-drop module. However, with increasing demands for bandwidth and network flexibility, multiple wavelengths may be broadcast or delivered to an end user, and then one wavelength (or potentially a small range of wavelengths) is selected by the end user. There is, therefore, a strong demand to provide an integrated module that combines a photodetector with a tunable optical filter, to select particular wavelength(s) from a multiple-wavelength DWDM optical signal, which also includes a transmitter or a group of transmitters to send a different wavelength or a band of different wavelengths back to the network. Furthermore, to meet the requirements and needs of short-distance optical systems, these tunable transceivers have to be compact, reliable, inexpensive, and producible on a large scale. There is also a demand for sub-assemblies of the above system that may not include all of the components of the system to serve as building blocks of the system.